This invention relates to thermal ink jet printing on demand, and more particularly to pagewidth thermal ink jet printheads of the type assembled from fully functional roofshooter type printhead subunits.
There are two general configurations for thermal, drop-on-demand, ink jet printheads. In one configuration, droplets are propelled from nozzles in a direction parallel to the flow of ink in ink channels and parallel to the surface of the bubble-generating heating elements of the printhead, such as, for example, the printhead configuration disclosed in U.S. Pat. No. Re. 32,572 to Hawkins et al. and schematically shown in FIG. 1. This configuration is sometimes referred to as edge or side shooters. The other thermal ink jet configuration propels droplets from nozzles in a direction normal to the surface of the bubble-generating heating elements such as, for example, the printhead disclosed in U.S. Pat. No. 4,568,953 to Aoki et al. This latter configuration is sometimes referred as a roofshooter and is schematically illustrated in FIG. 2. It can be seen that a fundamental difference lies in the direction of droplet ejection. The sideshooter configuration ejects droplets in the plane of the substrate having the heating elements, while the roofshooter ejects droplets out of the plane of the substrate having the heating elements and in a direction normal thereto.
U.S. Pat. No. Re. 32,572 to Hawkins et al. discloses a sideshooter configuration for a thermal ink jet printhead and several fabricating processes therefor. Each printhead is composed of two parts aligned and bonded together. One part is a substantially flat substrate which contains on the surface thereof a linear array of heating elements and addressing electrodes, and the second part is a substrate having at least one recess anisotropically etched therein to serve as an ink supply manifold when the two parts are bonded together. A linear array of parallel grooves are also formed in the second part so that one end of the grooves communicate with the manifold recess and the other ends are open for use as ink droplet expelling nozzles. Many printheads can be made simultaneously by producing a plurality of sets of heating element arrays with their addressing electrodes on a silicon wafer. A corresponding plurality of sets of channels and associated manifolds are produced in a second silicon wafer. The two wafers are aligned and bonded together and then diced into many separate printheads. The printheads may be used in carriage-type printers for printing swaths of information and then stepping the recording medium a distance of one swath and continuing to print adjacent swaths of information until a full page of information is printed. Alternatively, the printheads may be considered as subunits of a pagewidth printhead and arranged on a structural image bar for pagewidth printing. In pagewidth printing, the printheads may be assembled by abutting a plurality of the printhead subunits end-to-end on the image bar or staggering them on two separate image bars or on opposite sides of the same image bar.
U.S. Pat. No. 4,568,953 to Aoki et al. discloses a thermal ink jet printhead in which the droplets are ejected on demand through nozzles aligned above and parallel to the heating elements, so that the droplet trajectories are normal to the heating elements. In order to prevent nozzle clogging, the ink is circulated through the printhead and internal passageways having cross-sectional flow areas larger than the nozzles. This enables particulate matter larger than the nozzles to pass and be swept away by the circulating ink entering and leaving the printhead through inlet and outlet tubes.
U.S. Pat. No. 4,789,425 to Drake et al. discloses a roofshooter-type thermal ink jet printhead, wherein each printhead comprises a silicon heater plate and a fluid directing structural member. The heater plate has a linear array of heating elements, associated addressing electrodes, and an elongated ink-filled hole parallel with the heating element array. The structural member contains at least one recessed cavity, a plurality of nozzles, and a plurality of parallel walls within the recessed cavity which define individual ink channels for directing the ink to the nozzles. The recessed cavity and fill hole are in communication with each other and form the ink reservoir within the printhead. The ink holding capacity of the fill hole is larger than that of the recessed cavity. The fill hole is precisely formed and positioned within the heater plate by anisotropic etching. The structural member may be fabricated either from two layers of photoresist, a two-stage flat nickel electroform, or a single photoresist layer and a single stage flat nickel electroform.
U.S. Pat. No. 4,829,324 to Drake et al. discloses a large array ink jet printhead having two basic parts, one containing an array of heating elements and addressing electrodes on the surface thereof, and the other containing the liquid ink handling system. At least the part containing the ink handling system is silicon and is assembled from generally identical subunits aligned and bonded side-by-side on the part surface having the heating element array. In one embodiment a plurality of channel plate subunits are anisotropically etched in a silicon wafer and a plurality of heating element subunits are formed on another silicon wafer. The heating element wafer is also anisotropically etched with elongated slots. The wafers are aligned and bonded together, then diced into complete printhead subunits which have abutting side surfaces that are {111} planes for accurate side-by-side assembly.
U.S. Pat. No. 4,851,371 to Fisher et al. and U.S. Pat. No. 4,935,750 to Hawkins disclose a cost effective method of fabricating a large array or pagewidth silicon device having high resolution. The pagewidth device is assembled by abutting silicon device subunits such as image sensors or thermal ink jet printheads. For printheads, the subunits are fully functional small printheads comprising an ink flow directing channel plate and a heating element plate which are bonded together. A plurality of individual printhead subunits are obtained by dicing aligned and bonded channel wafers and heating element wafers. The abutting edges of the printhead subunits are diced in such a manner that the resulting kerfs have vertical to inwardly directed sides which enable high tolerance linear abutment of adjacent subunits. U.S. Pat. No. 4,935,750 discloses how a pagewidth printhead may be further stabilized and strengthened by assembly of printhead subunits on a flat structural member. Assembly of the pagewidth printhead is complete when an elongated hollow conduit means having a plurality of outlets is mounted over the subunits with each outlet aligned with a one of the inlets of the printhead subunits. Gaskets are sealed to the outlets of the conduit means by, for example, an adhesive earlier screened onto the gasket. The gasket sealingly surrounds the printhead subunit inlet and outlets of the conduit means and prevents the ink supplied to the printhead subunits via the conduit means from leaking at the interface therebetween.
U.S. Pat. No. 4,985,710 to Drake et al. discloses a "roofshooter" pagewidth printhead for use in a thermal ink jet printing device fabricated from a plurality of subunits, each being produced by bonding a heater substrate, having an architecture including an array of heater elements and an etched ink feed slot, to a secondary substrate having a series of spaced feed hole openings to form a combined substrate in which the series of spaced feed hole openings communicates with the ink feed slot, and dicing the combined substrates through the ink feed slot to form a subunit. An array of butted subunits having a length equal to one pagewidth is formed by butting one of the subunits against an adjacent subunit. The array of butted subunits is bonded to a pagewidth support substrate. The secondary substrate provides an integral support structure for maintaining the alignment of the heater plate which, if diced through the feed hole without the secondary substrate, would separate into individual pieces, thereby complicating the alignment and assembly process.